The 1955 Theatre Catalog and 1959 IMPA list it in Garwood MO (3 miles east of the drive-in) instead of Van Buren (9 miles southwest), but the 21’s Facebook page claims Van Buren. The 1972 IMPA puts the 21 in Ellington (17 miles north).

The 1959 IMPA lists capacity at 250, and the 1955 Catalog had it at 210. By the 1972 IMPA, it’s down to 200. In the 1982 IMPA, it jumps to 800. But when I look at the satellite view, I just don’t see how even 700 cars could fit.

Also, the 21 was still listed (in Ellington!) in the 1987 IMPA, so any closure probably came after that.